ABSTRACT
BTK inhibitors, Bcl-2 inhibitors, and other targeted therapies have significantly improved the outcomes of patients with chronic lymphocytic leukemia (CLL). With increased survivorship, monitoring disease and deciphering potential mechanisms of resistance to these agents are critical for devising effective treatment strategies. We used duplex sequencing, a technology that enables detection of mutations at ultra-low allelic frequencies, to identify mutations in five genes associated with drug resistance in CLL and followed their evolution in two patients who received multiple targeted therapies and ultimately developed disease progression on pirtobrutinib. In both patients we detected variants that expanded and reached significant cancer cell fractions (CCF). In patient R001, multiple known resistance mutations in both BTK and PLCG2 appeared following progression on zanubrutinib (BTK p.L528W, p.C481S; PLCG2 S707F, L845F, R665W, and D993H). In contrast, patient R002 developed multiple BTK mutations following acalabrutinib treatment, including known resistance mutations p.C481R, p.T474I and p.C481S. We found that pirtobrutinib was able to suppress, but not completely eradicate, BTK p.C481S mutations in both patients, but other resistance mutations such as mutations in PLCG2 and new BTK mutations increased while the patients were receiving pirtobrutinib. For example, BTK p.L528W in patient R001 increased in frequency more than 1,000-fold (from a CCF of 0.02% to 35%), and the CCF in p.T474I in patient R002 increased from 0.03% to 4.2% (more than 100-fold). Our data illuminate the evolutionary dynamics of resistant clones over the patients' disease course and under selective pressure from different targeted treatments.
Subject(s)
Leukemia, Lymphocytic, Chronic, B-Cell , Humans , Leukemia, Lymphocytic, Chronic, B-Cell/drug therapy , Leukemia, Lymphocytic, Chronic, B-Cell/genetics , Mutation , Clone Cells , Gene FrequencyABSTRACT
BACKGROUND: Individuals with germline BRCA1 and BRCA2 pathogenic variants (BRCA carriers) are at high risk of developing high grade serous ovarian carcinoma (HGSC). HGSC is predominantly driven by TP53 mutations, but mutations in this gene are also commonly found in non-cancerous tissue as a feature of normal human aging. We hypothesized that HGSC predisposition in BRCA carriers may be related to increased TP53 somatic evolution, which could be detectable by ultra-deep sequencing of TP53 mutations in gynecological liquid biopsies. METHODS: Duplex sequencing was used to identify TP53 mutations with high sensitivity in peritoneal washes and cervical liquid-based cytology (LBC) collected at surgery from 60 individuals including BRCA1 and BRCA2 carriers, and non-carriers. TP53 mutation pathogenicity was compared across groups and with TP53 cancer mutations. RESULTS: TP53 mutations were more abundant in cervical LBC than in peritoneal washes but increased with age in both sample types. In peritoneal washes, but not in cervical LBC, pathogenic TP53 mutation burden was increased in BRCA1 carriers compared to non-carriers, independently of age. Five individuals shared identical pathogenic TP53 mutations in peritoneal washes and cervical LBC, but not in blood. CONCLUSIONS: Ultra-deep sequencing of TP53 mutations in peritoneal washes collected at surgery reveals increased burden of pathogenic TP53 mutations in BRCA1 carriers. This excess of pathogenic TP53 mutations might be linked to the elevated risk of HGSC in these individuals. In some patients, concordant TP53 mutations were found in peritoneal washes and cervical LBCs, but the cell of origin remains unknown and deserves further investigation.
ABSTRACT
Mitochondrial DNA (mtDNA) is prone to mutation in aging and over evolutionary time, yet the processes that regulate the accumulation of de novo mtDNA mutations and modulate mtDNA heteroplasmy are not fully elucidated. Mitochondria lack certain DNA repair processes, which could contribute to polymerase error-induced mutations and increase susceptibility to chemical-induced mtDNA mutagenesis. We conducted error-corrected, ultra-sensitive Duplex Sequencing to investigate the effects of two known nuclear genome mutagens, cadmium and Aflatoxin B1, on germline mtDNA mutagenesis in Caenorhabditis elegans. Detection of thousands of mtDNA mutations revealed pervasive heteroplasmy in C. elegans and that mtDNA mutagenesis is dominated by C:G â A:T mutations generally attributed to oxidative damage. However, there was no effect of either exposure on mtDNA mutation frequency, spectrum, or trinucleotide context signature despite a significant increase in nuclear mutation rate after aflatoxin B1 exposure. Mitophagy-deficient mutants pink-1 and dct-1 accumulated significantly higher levels of mtDNA damage compared to wild-type C. elegans after exposures. However, there were only small differences in mtDNA mutation frequency, spectrum, or trinucleotide context signature compared to wild-type after 3050 generations, across all treatments. These findings suggest mitochondria harbor additional previously uncharacterized mechanisms that regulate mtDNA mutational processes across generations.
Subject(s)
Caenorhabditis elegans , DNA, Mitochondrial , Animals , DNA, Mitochondrial/genetics , Caenorhabditis elegans/genetics , Cadmium/toxicity , Aflatoxin B1/toxicity , Mutation Accumulation , Mitochondria/genetics , Mutation , Germ CellsABSTRACT
Polyguanine tracts (PolyGs) are short guanine homopolymer repeats that are prone to accumulating mutations when cells divide. This feature makes them especially suitable for cell lineage tracing, which has been exploited to detect and characterize precancerous and cancerous somatic evolution. PolyG genotyping, however, is challenging because of the inherent biochemical difficulties in amplifying and sequencing repetitive regions. To overcome this limitation, we developed PolyG-DS, a next-generation sequencing (NGS) method that combines the error-correction capabilities of duplex sequencing (DS) with enrichment of PolyG loci using CRISPR-Cas9-targeted genomic fragmentation. PolyG-DS markedly reduces technical artifacts by comparing the sequences derived from the complementary strands of each original DNA molecule. We demonstrate that PolyG-DS genotyping is accurate, reproducible, and highly sensitive, enabling the detection of low-frequency alleles (<0.01) in spike-in samples using a panel of only 19 PolyG markers. PolyG-DS replicated prior results based on PolyG fragment length analysis by capillary electrophoresis, and exhibited higher sensitivity for identifying clonal expansions in the nondysplastic colon of patients with ulcerative colitis. We illustrate the utility of this method for resolving the phylogenetic relationship among precancerous lesions in ulcerative colitis and for tracing the metastatic dissemination of ovarian cancer. PolyG-DS enables the study of tumor evolution without prior knowledge of tumor driver mutations and provides a tool to perform cost-effective and easily scalable ultra-accurate NGS-based PolyG genotyping for multiple applications in biology, genetics, and cancer research.
Subject(s)
Cell Lineage , DNA/genetics , Guanine/chemistry , Neoplasms/genetics , Poly G/genetics , Cell Differentiation , Clonal Evolution , DNA/chemistry , Genotype , HumansABSTRACT
Mutations in mitochondrial DNA (mtDNA) cause maternally inherited diseases, while somatic mutations are linked to common diseases of aging. Although mtDNA mutations impact health, the processes that give rise to them are under considerable debate. To investigate the mechanism by which de novo mutations arise, we analyzed the distribution of naturally occurring somatic mutations across the mouse and human mtDNA obtained by Duplex Sequencing. We observe distinct mutational gradients in GâA and TâC transitions delimited by the light-strand origin and the mitochondrial Control Region (mCR). The gradient increases unequally across the mtDNA with age and is lost in the absence of DNA polymerase γ proofreading activity. In addition, high-resolution analysis of the mCR shows that important regulatory elements exhibit considerable variability in mutation frequency, consistent with them being mutational 'hot-spots' or 'cold-spots'. Collectively, these patterns support genome replication via a deamination prone asymmetric strand-displacement mechanism as the fundamental driver of mutagenesis in mammalian DNA. Moreover, the distribution of mtDNA single nucleotide polymorphisms in humans and the distribution of bases in the mtDNA across vertebrate species mirror this gradient, indicating that replication-linked mutations are likely the primary source of inherited polymorphisms that, over evolutionary timescales, influences genome composition during speciation.
Subject(s)
Aging/genetics , DNA Replication , DNA, Mitochondrial/genetics , Genome, Mitochondrial , Germ-Line Mutation , Mitochondria/genetics , Mutation Accumulation , Aging/metabolism , Animals , Chromosome Mapping , DNA Polymerase gamma/deficiency , DNA Polymerase gamma/genetics , DNA, Mitochondrial/metabolism , Genetic Speciation , High-Throughput Nucleotide Sequencing , Humans , Male , Mice , Mice, Inbred C57BL , Mitochondria/metabolism , Mutation Rate , Polymorphism, Single NucleotideABSTRACT
The super-enhancers (SEs) of lineage-specific genes in B cells are off-target sites of somatic hypermutation. However, the inability to detect sufficient numbers of mutations in normal human B cells has precluded the generation of a high-resolution mutational landscape of SEs. Here we captured and sequenced 12 B cell SEs at single-nucleotide resolution from 10 healthy individuals across diverse ethnicities. We detected a total of approximately 9,000 subclonal mutations (allele frequencies <0.1%); of these, approximately 8,000 are present in the BCL6 SE alone. Within the BCL6 SE, we identified 3 regions of clustered mutations in which the mutation frequency is â¼7 × 10-4 Mutational spectra show a predominance of C > T/G > A and A > G/T > C substitutions, consistent with the activities of activation-induced-cytidine deaminase (AID) and the A-T mutator, DNA polymerase η, respectively, in mutagenesis in normal B cells. Analyses of mutational signatures further corroborate the participation of these factors in this process. Single base substitution signatures SBS85, SBS37, and SBS39 were found in the BCL6 SE. While SBS85 is a denoted signature of AID in lymphoid cells, the etiologies of SBS37 and SBS39 are unknown. Our analysis suggests the contribution of error-prone DNA polymerases to the latter signatures. The high-resolution mutation landscape has enabled accurate profiling of subclonal mutations in B cell SEs in normal individuals. By virtue of the fact that subclonal SE mutations are clonally expanded in B cell lymphomas, our studies also offer the potential for early detection of neoplastic alterations.
Subject(s)
B-Lymphocytes/metabolism , Enhancer Elements, Genetic/genetics , Proto-Oncogene Proteins c-bcl-6/genetics , Adult , Cell Line , Cytidine Deaminase/genetics , DNA Mutational Analysis/methods , DNA-Directed DNA Polymerase/genetics , Gene Frequency , Genetic Loci/genetics , Healthy Volunteers , Humans , Lymphoma, B-Cell/blood , Lymphoma, B-Cell/diagnosis , Lymphoma, B-Cell/genetics , Middle Aged , Mutation Rate , Proto-Oncogene Proteins c-bcl-6/metabolism , Young AdultABSTRACT
Human colorectal cancers (CRCs) contain both clonal and subclonal mutations. Clonal driver mutations are positively selected, present in most cells, and drive malignant progression. Subclonal mutations are randomly dispersed throughout the genome, providing a vast reservoir of mutant cells that can expand, repopulate the tumor, and result in the rapid emergence of resistance, as well as being a major contributor to tumor heterogeneity. Here, we apply duplex sequencing (DS) methodology to quantify subclonal mutations in CRC tumor with unprecedented depth (104) and accuracy (<10-7). We measured mutation frequencies in genes encoding replicative DNA polymerases and in genes frequently mutated in CRC, and found an unexpectedly high effective mutation rate, 7.1 × 10-7. The curve of subclonal mutation accumulation as a function of sequencing depth, using DNA obtained from 5 different tumors, is in accord with a neutral model of tumor evolution. We present a theoretical approach to model neutral evolution independent of the infinite-sites assumption (which states that a particular mutation arises only in one tumor cell at any given time). Our analysis indicates that the infinite-sites assumption is not applicable once the number of tumor cells exceeds the reciprocal of the mutation rate, a circumstance relevant to even the smallest clinically diagnosable tumor. Our methods allow accurate estimation of the total mutation burden in clinical cancers. Our results indicate that no DNA locus is wild type in every malignant cell within a tumor at the time of diagnosis (probability of all cells being wild type, 10-308).
ABSTRACT
Next-generation sequencing methods suffer from low recovery, uneven coverage, and false mutations. DNA fragmentation by sonication is a major contributor to these problems because it produces randomly sized fragments, PCR amplification bias, and end artifacts. In addition, oligonucleotide-based hybridization capture, a common target enrichment method, has limited efficiency for small genomic regions, contributing to low recovery. This becomes a critical problem in clinical applications, which value cost-effective approaches focused on the sequencing of small gene panels. To address these issues, we developed a targeted genome fragmentation approach based on CRISPR/Cas9 digestion that produces DNA fragments of similar length. These fragments can be enriched by a simple size selection, resulting in targeted enrichment of up to approximately 49,000-fold. Additionally, homogenous length fragments significantly reduce PCR amplification bias and maximize read usability. We combined this novel target enrichment approach with Duplex Sequencing, which uses double-strand molecular tagging to correct for sequencing errors. The approach, termed CRISPR-DS, enables efficient target enrichment of small genomic regions, even coverage, ultra-accurate sequencing, and reduced DNA input. As proof of principle, we applied CRISPR-DS to the sequencing of the exonic regions of TP53 and performed side-by-side comparisons with standard Duplex Sequencing. CRISPR-DS detected previously reported pathogenic TP53 mutations present as low as 0.1% in peritoneal fluid of women with ovarian cancer, while using 10- to 100-fold less DNA than standard Duplex Sequencing. Whether used as standalone enrichment or coupled with high-accuracy sequencing methods, CRISPR-based fragmentation offers a simple solution for fast and efficient small target enrichment.
Subject(s)
CRISPR-Cas Systems , Ovarian Neoplasms/genetics , Sequence Analysis, DNA/methods , Tumor Suppressor Protein p53/genetics , DNA/genetics , DNA Fragmentation , Female , High-Throughput Nucleotide Sequencing , HumansABSTRACT
Background: There are >14,500 structurally diverse per- and polyfluoroalkyl substances (PFAS). Despite knowledge that these "forever chemicals" are in 99% of humans, mechanisms of toxicity and adverse health effects are incompletely known. Furthermore, the contribution of genetic variation to PFAS susceptibility and health consequences is unknown. Objectives: We determined the toxicity of a structurally distinct set of PFAS in twelve genetically diverse strains of the genetic model system Caenorhabditis elegans. Methods: Dose-response curves for four perfluoroalkyl carboxylic acids (PFNA, PFOA, PFPeA, and PFBA), two perfluoroalkyl sulfonic acids (PFOS and PFBS), two perfluoroalkyl sulfonamides (PFOSA and PFBSA), two fluoroether carboxylic acids (GenX and PFMOAA), one fluoroether sulfonic acid (PFEESA), and two fluorotelomers (6:2 FCA and 6:2 FTS) were determined in the C. elegans laboratory reference strain, N2, and eleven genetically diverse wild strains. Body length was quantified by image analysis at each dose after 48 hr of developmental exposure of L1 arrest-synchronized larvae to estimate effective concentration values (EC50). Results: There was a significant range in toxicity among PFAS: PFOSA > PFBSA ≈ PFOS ≈ PFNA > PFOA > GenX ≈ PFEESA > PFBS ≈ PFPeA ≈ PFBA. Long-chain PFAS had greater toxicity than short-chain, and fluorosulfonamides were more toxic than carboxylic and sulfonic acids. Genetic variation explained variation in susceptibility to PFBSA, PFOS, PFBA, PFOA, GenX, PFEESA, PFPeA, and PFBA. There was significant variation in toxicity among C. elegans strains due to chain length, functional group, and between legacy and emerging PFAS. Conclusion: C. elegans respond to legacy and emerging PFAS of diverse structures, and this depends on specific structures and genetic variation. Harnessing the natural genetic diversity of C. elegans and the structural complexity of PFAS is a powerful New Approach Methodology (NAM) to investigate structure-activity relationships and mechanisms of toxicity which may inform regulation of other PFAS to improve human and environmental health.
ABSTRACT
RNA viruses, like SARS-CoV-2, depend on their RNA-dependent RNA polymerases (RdRp) for replication, which is error prone. Monitoring replication errors is crucial for understanding the virus's evolution. Current methods lack the precision to detect rare de novo RNA mutations, particularly in low-input samples such as those from patients. Here we introduce a targeted accurate RNA consensus sequencing method (tARC-seq) to accurately determine the mutation frequency and types in SARS-CoV-2, both in cell culture and clinical samples. Our findings show an average of 2.68 × 10-5 de novo errors per cycle with a C > T bias that cannot be solely attributed to APOBEC editing. We identified hotspots and cold spots throughout the genome, correlating with high or low GC content, and pinpointed transcription regulatory sites as regions more susceptible to errors. tARC-seq captured template switching events including insertions, deletions and complex mutations. These insights shed light on the genetic diversity generation and evolutionary dynamics of SARS-CoV-2.
Subject(s)
COVID-19 , Genome, Viral , Mutation , RNA, Viral , SARS-CoV-2 , Virus Replication , SARS-CoV-2/genetics , Humans , Virus Replication/genetics , COVID-19/virology , Genome, Viral/genetics , RNA, Viral/genetics , Sequence Analysis, RNA/methods , Evolution, Molecular , Mutation RateABSTRACT
Somatic TP53 mutations are prevalent in normal tissue but little is known about their association with cancer risk. Cervical liquid-based cytology (LBC), commonly known as Pap test, provides an accessible gynecological sample to test the value of TP53 somatic mutations as a biomarker for high-grade serous ovarian cancer (HGSC), a cancer type mostly driven by TP53 mutations. We used ultra-deep duplex sequencing to analyze TP53 mutations in LBC and blood samples from 70 individuals (30 with and 40 without HGSC) undergoing gynecologic surgery, 30 carrying BRCA1 or BRCA2 germline pathogenic variants (BRCApv). Only 30% of the tumor mutations were found in LBC samples. However, TP53 pathogenic mutations were identified in nearly all LBC and blood samples, with only 5.4% of mutations in LBC (20/368) also found in the corresponding blood sample. TP53 mutations were more abundant in LBC than in blood and increased with age in both sample types. BRCApv carriers with HGSC had more TP53 clonal expansions in LBC than BRCApv carriers without cancer. Our results show that, while not useful for direct cancer detection, LBC samples capture TP53 mutation burden in the gynecological tract, presenting potential value for cancer risk assessment in individuals at higher hereditary risk for ovarian cancer.
Subject(s)
BRCA1 Protein , BRCA2 Protein , Germ-Line Mutation , Ovarian Neoplasms , Tumor Suppressor Protein p53 , Humans , Female , Tumor Suppressor Protein p53/genetics , Germ-Line Mutation/genetics , Ovarian Neoplasms/genetics , Ovarian Neoplasms/blood , Ovarian Neoplasms/pathology , Ovarian Neoplasms/diagnosis , BRCA2 Protein/genetics , Middle Aged , BRCA1 Protein/genetics , Adult , Aged , Cervix Uteri/pathology , Biomarkers, Tumor/genetics , Biomarkers, Tumor/blood , CytologyABSTRACT
BACKGROUND: More than 70% of leiomyomas (LM) harbor MED12 mutations, primarily in exon 2 at c.130-131(GG). The cause of MED12 mutations in myometrial cells remains largely unknown. We hypothesized that increased ROS promotes MED12 mutations in myometrial cells through the oxidation of guanine nucleotides followed by misrepair. METHODS: Genomic oxidative burden (8-OHdG) was evaluated in vitro and in vivo by immunohistochemistry. MED12 mutations were examined by Sanger sequencing and deep sequencing. Transcriptome examined by RNA-seq was performed in myometrium with and without LM, in primary myometrial cells treated with ROS. 8-OHdG mediated misrepair was analyzed by CRISPR/Cas9. RESULTS: Uteri with high LM burden had a significantly higher rate of MED12 mutations than uteri with low LM burden. Compelling data suggest that the uterus normally produces reactive oxidative species (ROS) in response to stress, and ROS levels in LM are elevated due to metabolic defects. We demonstrated that genomic oxidized guanine (8-OHdG) was found at a significantly higher level in the myometrium of uteri that had multiple LM compared to myometrium without LM. Transcriptome and pathway analyses detected ROS stress in myometrium with LM. Targeted replacement of guanine with 8-OHdG at MED12 c.130 by CRISPR/Cas9 significantly increased the misrepair of G>T. Exposure of primary myometrial cells to oxidative stress in vitro increased misrepair/mutations as detected by duplex sequencing. CONCLUSIONS: Together, our data identified a clear connection between increased myometrial oxidative stress and a high rate of MED12 mutations that may underlie the risk of LM development and severity in women of reproductive age.
ABSTRACT
Both the SARS-CoV-2 virus and its mRNA vaccines depend on RNA polymerases (RNAP)1,2; however, these enzymes are inherently error-prone and can introduce variants into the RNA3. To understand SARS-CoV-2 evolution and vaccine efficacy, it is critical to identify the extent and distribution of errors introduced by the RNAPs involved in each process. Current methods lack the sensitivity and specificity to measure de novo RNA variants in low input samples like viral isolates3. Here, we determine the frequency and nature of RNA errors in both SARS-CoV-2 and its vaccine using a targeted Accurate RNA Consensus sequencing method (tARC-seq). We found that the viral RNA-dependent RNAP (RdRp) makes ~1 error every 10,000 nucleotides - higher than previous estimates4. We also observed that RNA variants are not randomly distributed across the genome but are associated with certain genomic features and genes, such as S (Spike). tARC-seq captured a number of large insertions, deletions and complex mutations that can be modeled through non-programmed RdRp template switching. This template switching feature of RdRp explains many key genetic changes observed during the evolution of different lineages worldwide, including Omicron. Further sequencing of the Pfizer-BioNTech COVID-19 vaccine revealed an RNA variant frequency of ~1 in 5,000, meaning most of the vaccine transcripts produced in vitro by T7 phage RNAP harbor a variant. These results demonstrate the extraordinary genetic diversity of viral populations and the heterogeneous nature of an mRNA vaccine fueled by RNAP inaccuracy. Along with functional studies and pandemic data, tARC-seq variant spectra can inform models to predict how SARS-CoV-2 may evolve. Finally, our results may help improve future vaccine development and study design as mRNA therapies continue to gain traction.
ABSTRACT
Mutations characterize diverse human cancers; there is a positive correlation between elevated mutation frequency and tumor progression. One exception is acute myeloid leukemia (AML), which has few clonal single nucleotide mutations. We used highly sensitive and accurate Duplex Sequencing (DS) to show now that AML, in addition, has an extensive repertoire of variants with low allele frequencies, < 1%, which is below the accurate detection limit of most other sequencing methodologies. The subclonal variants are unique to each individual and change in composition, frequency, and sequence context from diagnosis to relapse. Their functional significance is apparent by the observation that many are known variants and cluster within functionally important protein domains. Subclones provide a reservoir of variants that could expand and contribute to the development of drug resistance and relapse. In accord, we accurately identified subclonal variants in AML driver genes NRAS and RUNX1 at allele frequencies between 0.1% and 0.3% at diagnosis, which expanded to comprise a major fraction (14-53%) of the blast population at relapse. Early and accurate detection of subclonal variants with low allele frequency thus offers the opportunity for early intervention, prior to detection of clinical relapse, to improve disease outcome and enhance patient survival.
Subject(s)
Leukemia, Myeloid, Acute , Alleles , High-Throughput Nucleotide Sequencing/methods , Humans , Leukemia, Myeloid, Acute/diagnosis , Leukemia, Myeloid, Acute/genetics , Leukemia, Myeloid, Acute/pathology , Mutation , RecurrenceABSTRACT
Current screening methods for ovarian cancer (OC) have failed to demonstrate a significant reduction in mortality. Uterine lavage combined with TP53 ultra-deep sequencing for the detection of disseminated OC cells has emerged as a promising tool, but this approach has not been tested for early-stage disease or non-serous histologies. In addition, lavages carry multiple background mutations, the significance of which is poorly understood. Uterine lavage was collected preoperatively in 34 patients undergoing surgery for suspected ovarian malignancy including 14 patients with benign disease and 20 patients with OC (6 non-serous and 14 high grade serous-like (serous)). Ultra-deep duplex sequencing (~3000x) with a panel of common OC genes identified the tumor mutation in 33% of non-serous (all early stage) and in 79% of serous cancers (including four early stage). In addition, all lavages carried multiple somatic mutations (average of 25 mutations per lavage), more than half of which corresponded to common cancer driver mutations. Driver mutations in KRAS, PIK3CA, PTEN, PPP2R1A and ARID1A presented as larger clones than non-driver mutations and with similar frequency in lavages from patients with and without OC, indicating prevalent somatic evolution in all patients. Driver TP53 mutations, however, presented as significantly larger clones and with higher frequency in lavages from individuals with OC, suggesting that TP53-specific clonal expansions are linked to ovarian cancer development. Our results demonstrate that lavages capture cancer cells, even from early-stage cancers, as well as other clonal expansions and support further exploration of TP53 mutation burden as a potential OC risk factor.
Subject(s)
Ovarian Neoplasms , Therapeutic Irrigation , Humans , Female , Ovarian Neoplasms/genetics , Mutation/genetics , Clonal Evolution , Tumor Suppressor Protein p53/geneticsABSTRACT
PREMISE OF THE STUDY: Seed dispersal contributes to gene flow and is responsible for colonization of new sites and range expansion. Sequencing chloroplast haplotypes offers a way to estimate contributions of seed dispersal to population genetic structure and enables studies of population history. Whole-genome sequencing is expensive, but resources can be conserved by pooling samples. Unfortunately, haplotype associations among single-nucleotide polymorphisms (SNPs) are lost in pooled samples, and treating SNP allele frequencies as independent markers provides biased estimates of genetic structure. METHODS: We developed sampling methodologies and an application, CallHap, that uses a least-squares algorithm to evaluate the fit between observed and predicted SNP allele frequencies from pooled samples based on haplotype network phylogeny structure, thus enabling pooling for chloroplast sequencing for large-scale studies of chloroplast genomic variation. This method was tested using artificially constructed test networks and pools, and pooled samples of Lasthenia californica (California goldfields) from southern Oregon, USA. RESULTS: CallHap reliably recovered network topologies and haplotype frequencies from pooled samples. DISCUSSION: The CallHap pipeline allows for the efficient use of resources for estimation of genetic structure for studies using nonrecombining haplotypes such as intraspecific variation in chloroplast, mitochondrial, bacterial, or viral DNA.
ABSTRACT
PREMISE OF THE STUDY: Low-elevation surveys with small aerial drones (micro-unmanned aerial vehicles [UAVs]) may be used for a wide variety of applications in plant ecology, including mapping vegetation over small- to medium-sized regions. We provide an overview of methods and procedures for conducting surveys and illustrate some of these applications. METHODS: Aerial images were obtained by flying a small drone along transects over the area of interest. Images were used to create a composite image (orthomosaic) and a digital surface model (DSM). Vegetation classification was conducted manually and using an automated routine. Coverage of an individual species was estimated from aerial images. RESULTS: We created a vegetation map for the entire region from the orthomosaic and DSM, and mapped the density of one species. Comparison of our manual and automated habitat classification confirmed that our mapping methods were accurate. A species with high contrast to the background matrix allowed adequate estimate of its coverage. DISCUSSION: The example surveys demonstrate that small aerial drones are capable of gathering large amounts of information on the distribution of vegetation and individual species with minimal impact to sensitive habitats. Low-elevation aerial surveys have potential for a wide range of applications in plant ecology.
ABSTRACT
Long-lived adult stem cells could accumulate non-repaired DNA damage or mutations that increase the risk of tumor formation. To date, studies on mutations in stem cells have concentrated on clonal (homoplasmic) mutations and have not focused on rarely occurring stochastic mutations that may accumulate during stem cell dormancy. A major challenge in investigating these rare mutations is that conventional next generation sequencing (NGS) methods have high error rates. We have established a new method termed Duplex Sequencing (DS), which detects mutations with unprecedented accuracy. We present a comprehensive analysis of mitochondrial DNA mutations in human breast normal stem cells and non-stem cells using DS. The vast majority of mutations occur at low frequency and are not detectable by NGS. The most prevalent point mutation types are the C>T/G>A and A>G/T>C transitions. The mutations exhibit a strand bias with higher prevalence of G>A, T>C, and A>C mutations on the light strand of the mitochondrial genome. The overall rare mutation frequency is significantly lower in stem cells than in the corresponding non-stem cells. We have identified common and unique non-homoplasmic mutations between non-stem and stem cells that include new mutations which have not been reported previously. Four mutations found within the MT-ND5 gene (m.12684G>A, m.12705C>T, m.13095T>C, m.13105A>G) are present in all groups of stem and non-stem cells. Two mutations (m.8567T>C, m.10547C>G) are found only in non-stem cells. This first genome-wide analysis of mitochondrial DNA mutations may aid in characterizing human breast normal epithelial cells and serve as a reference for cancer stem cell mutation profiles.
Subject(s)
DNA, Mitochondrial/genetics , High-Throughput Nucleotide Sequencing/methods , Mammary Glands, Human/cytology , Mutation , Stem Cells/metabolism , Adult , Alleles , DNA Mutational Analysis/methods , Female , Gene Frequency , Genome, Mitochondrial , Genotype , Healthy Volunteers , Humans , Open Reading Frames , Young AdultABSTRACT
Duplex Sequencing (DS) is a next-generation sequencing methodology capable of detecting a single mutation among >1 × 10(7) wild-type nucleotides, thereby enabling the study of heterogeneous populations and very-low-frequency genetic alterations. DS can be applied to any double-stranded DNA sample, but it is ideal for small genomic regions of <1 Mb in size. The method relies on the ligation of sequencing adapters harboring random yet complementary double-stranded nucleotide sequences to the sample DNA of interest. Individually labeled strands are then PCR-amplified, creating sequence 'families' that share a common tag sequence derived from the two original complementary strands. Mutations are scored only if the variant is present in the PCR families arising from both of the two DNA strands. Here we provide a detailed protocol for efficient DS adapter synthesis, library preparation and target enrichment, as well as an overview of the data analysis workflow. The protocol typically takes 1-3 d.